1. Field of the Invention
The present invention relates to a bottom link type front wheel suspension for a motorcycle.
2. Description of Related Art
The front wheel suspension for a motorcycle is generally of a telescopic type or a bottom link type.
The telescopic type front wheel suspension is configured such that a front wheel is directly connected to a body frame by means of a damper. When using the telescopic front wheel suspension for a large-sized motorcycle, a large stroke damper, that is, a large-sized damper is required to obtain a large ascending/descending stroke of a front wheel. When using a small stroke damper, the bottom link type front wheel suspension is relatively superior to the telescopic type front wheel suspension since the stroke of the damper corresponding to the ascending/descending stroke of the front wheel can be decreased by use of the link structure.
The telescopic type suspension has an expandable structure capable of being expanded/contracted just like a telescope, and is suitable for a motorcycle having a relatively small caster angle (angle between vertical line and front fork).
For a motorcycle having a large caster angle, which is so-called an American bike, since the front fork is largely tilted in the horizontal direction, it is difficult to absorb the vertical movement amount of a front wheel by the telescopic suspension from the viewpoint of the mounting angle of the telescopic suspension. In this regard, since the bottom link type suspension is less affected by the caster angle, it is suitable for a motorcycle having a larger caster angle.
A bottom link type front wheel suspension for a motorcycle has been disclosed, for example, in Japanese Utility Model Publication No. Sho 60-15744 entitled xe2x80x9cFront Wheel Suspension For Two-Wheeled Vehicle.xe2x80x9d The above-described related art bottom link type front wheel suspension is classified into a leading arm type shown in FIG. 1 of the above document (hereinafter, referred to as xe2x80x9crelated art No. 1xe2x80x9d), and a trailing arm type shown in FIG. 2 of the above document (hereinafter, referred to as xe2x80x9crelated art No. 2xe2x80x9d).
The related art Nos. 1 and 2 will be briefly described below. It should be noted that in the following description, reference characters cited from the above document are used. The related art No. 1 is characterized in that the rear end of a leading arm 3 is connected to the lower portion of a front fork F, and a front wheel W is mounted to the front end of the leading arm 3; and the rear end of a control lever 6 is connected to the front end of a lower bridge Fb and the front end of the control lever 6 is connected to the front end of an upper bridge Fa by means of a damper A. Accordingly, the damper A is protruded forwardly from the front fork F. The related art No. 1 is also characterized in that a middle point of the control lever 6 in the longitudinal direction is connected to a middle point of the leading arm 3 in the longitudinal direction by means of a link 8.
The related art No. 2 is characterized in that the front end of the leading arm 3 is connected to the lower portion of the front fork F and the front wheel W is mounted to the rear end of the leading arm 3 , and the front end of the control lever 6 is connected to a middle point of the front fork F and the rear end of the control lever 6 is connected to the front end of the upper bridge Fa by means of the damper A. Accordingly, the upper half of the damper A is protruded forwardly from the front fork F. The related art No. 2 is also characterized in that a middle point of the control lever 6 in the longitudinal direction is connected to a middle point of the leading arm 3 in the longitudinal direction by means of a link 8.
The related art No. 1 is problematic in that since the damper A is protruded forwardly from the front fork F as described above, a space for disposing the damper A is required to be provided in front of the front fork F. This results in that arrangement of a headlamp, a meter and the like in front of the front fork F is restricted in design. The same is true for the related art No. 2.
It may be considered to dispose the damper A at the back of the front fork F, however, in this case, a fuel tank and the like are accommodated at the back of the front fork F, presenting the same restriction in design.
FIG. 15 is a view, equivalent to FIG. 2 of the above document, illustrating the principle of the related art typical bottom link type suspension. Reference numerals are newly appended to the elements in FIG. 15.
One end of a front wheel supporting arm 102 is swingably mounted to the lower end of a front forked portion 101; an axle 104 of a front wheel 103 is mounted to the leading end of the front wheel supporting arm 102, a push rod 105 is erected from a middle point of the front wheel supporting arm 102; the upper portion of the push rod 105 is connected to another link 106 extending from the upper portion of the front forked portion 101; and the leading end of the link 106 is connected to the lower ends of a suspension spring 107 and a hydraulic damper (not shown). With this configuration, the front wheel 103 is suspended from a parallel link structure, and when the front wheel 103 is moved up or down, the axle 104 is moved from a position (1) to a position (2) or from the position (1) to a position (3).
With the above parallel link structure, the motion of the link 106 desirably follows the motion of the front wheel supporting arm 102, that is, the motion of the axle 104, and accordingly, the axle 104 can be desirably supported by the suspension spring 107 to which the leading end of the link 106 is connected. On the other hand, in the above parallel link structure, since the upward motion of the axle 104 simply corresponds to the compression motion of the suspension spring 107, the characteristic of the suspension spring 107 must be simply determined depending on the motion of the axle 104. This causes a problem in that the degree of freedom in design of the suspension spring 107 becomes poor.
Furthermore, to keep the parallel link structure, the push rod 105 must be disposed in such a manner as to be substantially in parallel with the front forked portion 101 and to be made as apart from the front forked portion 101 as possible. Accordingly, when a vehicular body is viewed from a side surface thereof, the push rod 105 becomes conspicuous, with a result that the external appearance of the front wheel suspension is degraded. To cope with such an inconvenience, it is required to adopt a structure shown in FIG. 15 in which a protrusion member 108 is provided in front of the upper portion of the front forked portion 101 while the push rod 105 is made as close to the front forked portion 101 as possible. Consequently, as shown in FIG. 2 of the above document, the front forked portion must be designed to have a complicated triangular structure.
An object of the present invention is to provide a bottom link type front wheel suspension capable of allowing accessories such as a headlamp and a meter to be easily arranged in front of a front fork. Furthermore, an object of the present invention is to provide a front wheel suspension for a two-wheeled vehicle, which is capable of enhancing the external appearance of the front wheel suspension without complicating a structure of a front fork and its vicinity by improving a link structure, and also enlarging the degree of freedom of the suspension spring.
To achieve the above object, according to a first aspect of the present invention, there is provided a bottom link type front wheel suspension for a motorcycle, characterized in that: a steering stem is rotatably mounted in a head pipe; a top bridge and a bottom bridge are mounted on upper and lower portions of the steering stem, respectively; upper ends of front forked portions are mounted to the top and bottom bridges; one-ends of front wheel supporting arms are connected to lower ends of the front forked portions; lower ends of rods are connected to middle points of the front wheel supporting arms; an arm vertically swingably extending forwardly from the bottom bridge is connected to the upper ends of the rods; lower ends of dampers are connected to the arm; and the upper ends of the dampers are connected to the top bridge side; wherein the center of the damper substantially corresponds to the center of the front forked portion in a side view.
In the above bottom link type front wheel suspension, the arm swingably extends forwardly from the bottom bridge, and the lower ends of the dampers are connected to the arm and the upper ends of the dampers are connected to the top bridge side; and further, the center of the damper substantially corresponds to the center of the front forked portion in a side view.
Accordingly, the dampers are not protruded forwardly from the front forked portions in the range of the swing angle of the arm, with a result that a space remains in front of the front forked portions and accessories such as a headlamp and a meter can be arranged in the space.
According to a second aspect of the present invention, there is provided a front wheel suspension for a two-wheeled vehicle, characterized in that: front wheel supporting arms are swingably mounted to front forked portions; an axle of a front wheel is mounted to leading ends of the front wheel supporting arms; push rods are erected from middle points of the front wheel supporting arms, upper ends of the push rods are connected to one end or in the vicinity of an upper link disposed near a bottom bridge; the other end of the upper link is swingably mounted to the bottom bridge; and the upper link is connected to the lower end of a suspension spring, whereby when a vehicular body is viewed from the side surface thereof, one end of the upper link extends to a position substantially overlapped with the front forked portions, and thereby each of the front supporting arms, each of the push rods, and the upper link constitute a Z-shaped link.
The front wheel suspension, which is basically of a bottom link type, has a Z-shaped link structure including each of the front wheel supporting arms, each of the push rods, and the upper link. Accordingly, it is possible to make the upper portion of the push rod closer to the front forked portion, and hence to improve the external appearance of the front wheel suspension without complicating the structure of the front forked portion and its vicinity.
Furthermore, since the front wheel suspension has the Z-shaped link structure, it is possible to freely select the lengths, mounting postures, and the relative angles of the constituents, and hence to increase the degree of freedom in design of the suspension spring.
According to a third aspect of the present invention, in addition to the configuration of the second aspect of the present invention, a pivot for mounting the front wheel supporting arm to the front forked portion is offset to the rear wheel side from the center of the front forked portion.
Since the pivot of the front forked portion is offset to the rear wheel side, the lower portion of the push rod can be separated from the front forked portion to ensure a space for containing a part constituting the front wheel suspension.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.